The invention relates to vacuum street sweepers, including the motorized vehicular type having a hopper for receiving debris and a vacuum system for suctioning debris and depositing same in the hopper.
Vacuum street sweepers typically have a filtering screen inside the hopper, providing single stage filtration. This type of filtration involves a trade-off of air pollution versus vacuum suctioning power. If the screen inside the hopper is made very fine, air pollution and emission of particulate matter is reduced, but so is vacuum suctioning power. Furthermore, there is increased likelihood of the screen becoming obstructed by mud. If the screen inside the hopper is made very coarse, vacuum suctioning power is maintained, but air pollution is increased. Furthermore, the larger particulate matter emitted through the system decreases blower life.
One type of known dust filtering system utilizes the filter bag technique wherein a plurality of tubes of filtration material limit dust emission. This system is objectionable because of high cost and difficulty in cleaning the bags.
The present invention addresses and solves the need for a cost effective vacuum street sweeper filtration system affording both high vacuum suctioning power and low air pollution emission. The invention further facilitates prolonged blower life and reduced screen-clogging. The entire filtration system of the invention is particularly easy to clean and maintain.